Described herein is a process and code system for embedding machine readable information on an object. The code is binary based, and uses different shapes and/or colors to encode the information. The code may be formed using fluorescent marking materials such as fluorescent inks or toners.
For example, described is machine readable code formed with fluorescent marking materials that can, by irradiation with radiation of an appropriate wavelength, be made to fluoresce to either be rendered visible or to be rendered to have a different color from the ink in ambient light, in a reversible process. Also described are information embedding code systems comprised of dots of glyphs fluorescing with different colors, substrates having information embedded thereon using the fluorescent marking materials, and systems for imprinting and reading the embedded information.
A number of advantages are associated with the various embodiments described herein. For example, where the fluorescent materials are colorless in normal room light (ambient light) conditions, the machine readable or encrypted information is invisible. The information is thus hidden until exposed to radiation such as UV light that causes the fluorescent materials to fluoresce. Another advantage is that the encrypted information, in the form of, for example, dots or glyphs, can not be copied with existing photocopiers. A further advantage is that where dots are used to encrypt the information, the amount of information that can be encrypted increases significantly because the number of dots that may be printed on the same page is much higher when compared with glyphs, and the size of the dots may be significantly decreased by using emissive (fluorescent) technology rather than a reflective technology.
U.S. Pat. No. 5,710,420, incorporated herein by reference in its entirety, describes a method of embedding and recovering machine readable information on a substrate which comprises (a) writing data in a predetermined machine readable code format on the substrate with a photochromic marking material having a first state corresponding to a first absorption spectrum and a second state corresponding to a second absorption spectrum; and (b) thereafter effecting a photochromic change in at least some of the photochromic marking material from the first state to the second state. Use of a photochromic marking material, which is a reflective technology, is thus described.
While known compositions and processes are suitable for their intended purposes, a need remains for additional systems and processes for embedding and recovering machine readable information on an object. Further, there is a need for systems and processes which enable the placement of encoded information on documents which is not detectable to the reader but which is machine readable. Additionally, there is a need for systems of encoding machine readable information so that larger amounts of such information may be stored, and the amount of overdetermination built into the stored information may be increased.